Quantum chemical investigations of surface chemistry with a hierarchy of cluster models

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Krishnan Raghavachari is supported by an award from the Theoretical and Computational Chemistry program to develop theoretical methods for studying surface chemistry by developing and applying a set of hierarchical theoretical models. The hierarchical concept involves the use of highly accurate methodology on small systems to validate more approximate and computationally cost effective methodologies for investigating complex systems. Building on prior work in the PI's research group, Raghavachari and coworkers are developing more sophisticated and broadly applicable methods in three areas: (1) accurate thermochemical models applicable for 3d and 4d transition metal elements and fourth-row main group elements. These methods are based on the successful Gaussian-n (Gn) models, but will include many improvements to overcome known deficiencies; (2) divalent pseudoatom parameters to enable accurate and efficient calculations for investigating chemistry on (100) surfaces of tetrahedrally bonded systems; (3) new electronic embedding methods for an accurate treatment of QM/QM multilayer calculations based on the popular ONIOM framework. These developments are applied to a range of applications on semiconductor and metal-oxide surface chemistry, including (1) controlled functionalization of Si(100) surfaces, (2) alloy growth of compound semiconductor surfaces, (3) reactions of biomolecules on silica surfaces, and (4) catalytic mechanisms of titanium oxide and vanadium oxide surfaces. The computer codes developed in this program are available to the scientific community as part of the Gaussian software package as well as in a set of freely available codes on the PI's website.